Require Import ZArith. Record plane : Set := point {abscissa : Z; ordinate : Z}. Open Scope Z_scope. Definition manhattan_dist (p1 p2 : plane) : Z := (Zabs (abscissa p1 - abscissa p2)) + (Zabs (ordinate p1 - ordinate p2)). Eval compute in (manhattan_dist (point 2 5) (point 7 (-9))).